It appears that the Anglican and Catholic Churches have come to an agreement on "mixed marriages" in 1975.
Anglican-Roman Catholic Commission on the Theology of Marriage and its Application to Mixed Marriages Final Report (June 1975)
Based on the summary linked in the joint document, both churches recognize mixed marriages, and by this agreement neither bans nor prohibits them. There should not be a problem in the nuptials proceeding as announced.
You are incorrect regarding your last presumption.
According to the current Canon Law, the sacrament of marriage is conferred on two baptized people. Since the Roman Catholic Church recognizes the Anglican baptism as using proper Trinitarian form and water, it is a simple matter of adhering to the guidelines contained therein and thus seeking (and most likely receiving) the waiver/dispensation (as I did; I married a Catholic when I was not Catholic). It's not that hard. It can be a difficulty of one of the parties is not willing to accept the three points listed below. (My room mate from college had initial objections when was to marry a young lady who was Catholic and he was not, but they worked it out as part of the pre Cana process).
CHAPTER VI. MIXED MARRIAGES
Can. 1124 Without express permission of the competent authority, a
marriage is prohibited between two baptized persons of whom one is
baptized in the Catholic Church or received into it after baptism and
has not defected from it by a formal act and the other of whom is
enrolled in a Church or ecclesial community not in full communion with
the Catholic Church.
Can. 1125 The local ordinary can grant a permission of this kind if
there is a just and reasonable cause. He is not to grant it unless
the following conditions have been fulfilled:
1/ the Catholic party is to declare that he or she is prepared to
remove dangers of defecting from the faith and is to make a sincere
promise to do all in his or her power so that all offspring are
baptized and brought up in the Catholic Church;
2/ the other party is to be informed at an appropriate time about the
promises which the Catholic party is to make, in such a way that it is
certain that he or she is truly aware of the promise and obligation of
the Catholic party;
3/ both parties are to be instructed about the purposes and essential
properties of marriage which neither of the contracting parties is to
exclude.
I foundThere is an American side guide to "Anglican/Roman Catholic" mixed marriage guidance, but haveI did not yet found one formfind an equivalent guide for the home country of the Anglican faith.